Compounds having an intense absorption in a wavelength range of 450 to 1100 nm, especially those having an absorption peak wavelength (λmax) between 480 nm and 620 nm, are used as an optical element in an optical recording layer of optical recording media including DVD-Rs, in an optical filter of image displays including liquid crystal displays (LCDs), plasma display panels (PDPs), electroluminescent displays (ELDs), cathode ray tube displays (CRTs), fluorescent display tubes, and field emission displays (FEDs), or in a CCD or CMOS image sensor.
The optical element of an image display is exemplified by a light absorber used in a color filter. An image display achieves a full color display using combinations of three primary colors of light, red, blue, and green. Light for displaying a color image contains a component that causes display quality reduction, such as light rays between green and red (550 to 600 nm) and a component that causes malfunction of an infrared remote controller (750 to 1100 nm). Then, an image display is equipped with an optical filter containing a light absorbing compound (light absorber) capable of selectively absorbing these unnecessary components of light.
A function to prevent reflection of ambient light, such as a fluorescent lamp, is also demanded in an optical filter. To prevent reflection of ambient light, an optical filter is required to absorb light with wavelengths of from 480 to 500 nm as well as the above-described unnecessary light components. Light in the recited wavelength range is near bright lines necessary to achieve image display. Accordingly, the light absorber to be used should have an especially narrow absorption band, i.e., a small half band width at λmax. The light absorber is also required to withstand light and heat and continue to function.
Optical filters containing a light absorber that have been proposed to data include an optical filter containing a dipyromethene metal chelate compound having a maximum absorption wavelength of 440 to 510 nm (see Patent Document 1) and an optical filter containing a porphyrin compound having a maximum absorption wavelength of 440 to 510 nm (see Patent Document 2). These light absorbing compounds, however, are not good in view of their absorption wavelength characteristics or affinity for a solvent or a binder resin, and the optical filters containing them do not exhibit sufficient performance in a wavelength range of 480 to 500 nm.
Wavelengths of semiconductor lasers used in writing and reading information on the aforementioned optical recording media are in the ranges of 750 to 830 nm for CD-Rs and of 620 to 690 nm for DVD±Rs. In pursuit of a further increased capacity, optical discs using shorter wavelength lasers have been under study. For example, those using a write wavelength of 380 to 420 nm have been studied.
Various kinds of compounds are useful to form an optical recording layer of optical recording media for short wavelength lasers. For example, Patent Document 3 discloses a cyanine compound, Patent Document 4 reports a metal complex of a triazole compound, and Patent Document 5 reports a porphyrin compound. These compounds, however, are problematic for use as an optical recording material forming an optical recording layer in view of their poor affinity particularly to a metal reflective film and resistance to moist heat.
Patent Document 1: JP 2003-57436A
Patent Document 2: JP 2004-45887A
Patent Document 3: JP 2001-301333A
Patent Document 4: JP 2004-174838A
Patent Document 5: JP 2005-59601A